Aqueous polyurethane dispersions containing dimer/trimer

ABSTRACT

The present invention relates to a composition being an aqueous dispersion of a polyurethane in water, said composition comprising water and the reaction product of (a) a water-dispersible isocyanate-terminated polyurethane prepolymer having an NCO content of between 2.1 and 10% by weight, (b) an organic polyisocyanate adduct mixture comprising a polyisocyanate dimer and a polyisocyanate trimer and having an average isocyanate functionality of between 2.1 and 4.0, and (c) an active hydrogen-containing chain extender. Also disclosed is a process for preparing this composition, and a method for coating a substrate with the composition.

This application is a division of application Ser. No. 08/265,369, filedJun. 24 , 1994 allowed.

FIELD OF THE INVENTION

This invention relates generally to aqueous polyurethane dispersions,and more particularly, to aqueous polyurethane dispersions that containpolyisocyanate dimer and trimer and are useful as coating compositions.

BACKGROUND OF THE INVENTION

Aqueous polyurethane dispersions are well known and are used in theproduction of a variety of useful polyurethane products, including, forexample, coatings, films, adhesives, sealants, and the like,collectively referred to as so-called "ACES". Such dispersions aretypically produced by dispersing a water-dispersible,isocyanate-terminated polyurethane prepolymer in an aqueous mediumtogether with an active hydrogen containing chain extender, such as adiamine.

The prepolymers used in the preparation of the dispersions are generallysubstantially linear, that is to say difunctional, and are typicallyobtained by reacting an excess of a diisocyanate with anisocyanate-reactive component comprising a polymeric diol in thepresence of a reactive compound, for example a diol or diisocyanate,containing an ionic or nonionic hydrophilic group or site.

Attempts to introduce higher functionality into the dispersedpolyurethanes, in an effort to enhance the physical properties of theresulting ACES or shorten the curing time for these products, have notbeen entirely successful. One method of increasing the functionality isby incorporating a higher functionality polyol, such as a triol ortetrol, into the prepolymer, and the use of such polyfunctional activehydrogen compounds in the preparation of ionic polyurethane dispersionshas been described in U.S. Pat. No. 4,554,308. The amount ofpolyfunctionality that can be introduced in this way is limited by thetendency of the more highly crosslinked prepolymers to gel and to formlarge micelles when dispersed, resulting in poor film-forming propertiesfor this dispersion.

Another method of introducing higher functionality employs a linearprepolymer in conjunction with a trifunctional chain extender, such asdiethylene triamine. This approach has been described in U.S. Pat. Nos.4,203,883 and 4,408,008. One problem associated with these triaminecross-linked urethane dispersions is that they tend to form gels priorto use and they tend to provide poor coalescence of the films onsubstrates during use.

Yet another method of introducing higher functionality uses atriisocyanate in the prepolymer preparation, but this methodology causessimilar problems to those that result when using a triol or tetrol inthe preparation of the prepolymer, including gelation and poordispersion of the prepolymer due to large micelle formation.

A different method of incorporating triisocyanates has been described inU.S. Pat. No. 4,507,431 which describes a process for preparing aqueousdispersions of cross-linked polyurethane ionomers. These dispersions aremade by mixing an isocyanate containing prepolymer dissolved in awater-miscible organic solvent having a boiling point of from 20 to 100°C. with a polyfunctional polyisocyanate cross-linking compound having anisocyanate functionality of about 2.2 to 4. The isocyanate-containingprepolymer is prepared from a linear polyhydroxy compound having amolecular weight of from 800 to 5000, and the prepolymer has exclusivelyaliphatic or cycloaliphatic terminal isocyanate groups in amounts from0.1 to 2% by weight incorporated therein by employing an aliphaticdiisocyante and/or cycloaliphatic diisocyanate compound alone as thediisocyanate reactant with said polyhyroxy compound or in conjunctionwith a non-aliphatic or non-cycloaliphatic diisocyanate reactant, andcontaining salt groups in amounts of from 0.02 to 1% by weight; so thatthere are from 0.1 to 1.5 isocyanate groups of said polyisocyanate perisocyanate group of said prepolymer; dispersing the resulting solutionin from 40 to 80% by weight, based on the polyurethane prepolymer andthe polyisocyanate, of water and evaporating the organic solvent.Unfortunately, evaporation of the solvent in the production of theaqueous dispersion in accordance with the teachings of the '431 patentis undesirable from an environmental standpoint.

Still another method of preparing aqueous polyurethane dispersions isdisclosed in U.S. Pat. No 5,169,895. The '895 patent discloses anaqueous dispersion of a water-dispersible polyurethane, wherein thepolyurethane represents the reaction product of (a) a water-dispersibleisocyanate-terminated polyurethane prepolymer having an NCO content of2.1 to 10% by weight, (b) an organic polyisocyanate having an averageisocyanate functionality of 2.1 to 4.0, and (c) an activehydrogen-containing chain extender, but with the proviso that thepolyurethane is prepared in the absence of the steps recited to preparethe polyurethane dispersion in the above-described '431 patent. Examplesof the organic polyisocyanate of component (b) of the '895 patentinclude the trimers of hexamethylene diisocyanate (so-called "HDI"),isophorone diisocyanate (so-called "IPDI"), and 2,4-toluenediisocyanate, biuret-modified HDI, and the adduct of 2,4-toluenediisocyanate and trimethylolpropane, as recited at column 5, lines 27-31of the '895 patent.

New aqueous dispersions of polyurethanes providing improved physicalproperties for ACES applications, relative to the above-described priorart compositions such as those described in the '895 patent, would behighly desired by the ACES community. The present invention provides onesuch improved composition.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a composition being anaqueous dispersion of polyurethane in water, said composition comprisingwater and the reaction product of:

(a) a water-dispersible isocyanate-terminated polyurethane prepolymerhaving an NCO content of between about 1.5 and 10% by weight,

(b) an organic polyisocyanate adduct mixture comprising a dimer and atrimer (also referred to herein as "dimer/trimer") and having an averageisocyanate functionality of between 2.1 and 4.0, and

(c) an active hydrogen-containing chain extender.

In another aspect, the present invention relates to a process forpreparing an aqueous dispersion of polyurethane which comprisesreacting, in an aqueous medium, a reaction mixture comprising:

(a) a water-dispersible isocyanate-terminated polyurethane prepolymerhaving an NCO content of between about 1.5 and 10% by weight,

(b) an organic polyisocyanate adduct mixture comprising a dimer and atrimer and having an average isocyanate functionality of between 2.1 and4.0, and

(c) an active hydrogen-containing chain extender.

In yet another aspect, the present invention relates to a method forcoating a substrate which comprises contacting the substrate with acoating composition comprising a dispersion in water of the reactionproduct of:

(a) a water-dispersible isocyanate-terminated polyurethane prepolymerhaving an NCO content of between about 1.5 and 10% by weight,

(b) an organic polyisocyanate adduct mixture comprising a dimer and atrimer and having an average isocyanate functionality of between 2.1 and4.0, and

(c) an active hydrogen-containing chain extender.

Preferably, the water-dispersible isocyante-terminated polyurethaneprepolymer (i.e., component (a) described in the above-mentionedcomposition, process and method claims) comprises the reaction productof:

(i) an organic diisocyanate;

(ii) a polyol component comprising a polymeric diol having a molecularweight in the range from 250 to 5000, and

(iii) a compound containing a hydrophilic center and at least twoisocyanate or isocyanate-reactive groups.

In other aspects of the present invention, components (a) and (b)employed in the above described composition, process and method, aresuitably combined, to provide a polyurethane prepolymer having at leasta portion of the dimer and the trimer incorporated into the prepolymer.

These and other aspects will become apparent upon reading the followingdetailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

It has now been surprisingly found by the present inventors inaccordance with the present invention that the use of a polyisocyanateadduct mixture comprising an isocyanate dimer and an isocyanate trimer,together with a water-dispersible isocyanate-terminated polyurethaneprepolymer, in the preparation of aqueous polyurethane dispersions,provides a polyurethane that, in use for example in ACES applications,exhibits enhanced physical properties, including increased tensilestrength and elongation, relative to the properties provided by priorart water-dispersible polyurethanes. Further, increasing the trimercontent of the polyisocyante adduct mixture, relative to the dimercontent, enables the production of ACES coatings having a high initialmodulus without being brittle.

The polyisocyanate used in making the isocyanate-terminated prepolymeremployed in the present invention may be aliphatic, cycloaliphatic,araliphatic or aromatic polyisocyanate. Examples of suitablepolyisocyanates include ethylene diisocyanate, 1,6-hexamethylenediisocyanate, isophorone diisocyanate, cyclohexane-1,4-diisocyanate,4,4'-dicyclohexylmethane diisocyanate, m- and p-tetramethylxylenediisocyanates, p-xylene diisocyanate, 1,4-phenylene diisocyanate,2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethanediisocyanate, 2,4'-diphenylmethane diisocyanate, polymethylenepolyphenyl polyisocyanates, 5-naphthalene diisocyanate. Mixtures ofpolyisocyanates can be used and also polyisocyanates which have beenmodified by the introduction of urethane, allophanate, urea, biuret,carbodiimide, uretonimine or isocyanurate residues.

The polyol employed to make the isocyanate-terminated prepolymer issuitably a high molecular weight polyol, preferably having a numberaverage molecular weight (M_(n)) of between about 400 and about 10,000,preferably between 400 and 3,000. Examples of the high molecular weightcompounds include:

1) Polyhydroxy polyesters which are obtained from polyhydric, preferablydihydric alcohols to which trihydric alcohols may be added andpolybasic, preferably dibasic carboxylic acids. Instead of thesepolycarboxylic acids the corresponding carboxylic acid anhydrides orpoly carboxylic acid esters of lower alcohols or mixtures thereof may beused for preparing the polyesters. The polycarboxylic acids may bealiphatic, cycloaliphatic, aromatic and/or heterocyclic and they may beunsaturated and/or substituted, e.g. by halogen atoms. Examples of theseacids include succinic acid, adipic acid, suberic acid, azelaic acid,sebacid acid, phthalic acid, isophthalic acid, trimellitic acid,phthalic acid anhydride, tetrahydrophthalic acid anhydride,hexahydrophthalic acid anhydride, tetrachlorophthalic acid anhydride,endomethylene tetrahydrophthalic acid anhydride, glutaric acidanhydride, maleic acid, maleic acid anhydride, fumaric acid, dimeric andtrimeric fatty acids such as oleic acid (which may be mixed withmonomeric fatty acids), dimethyl terephthalate and bis-glycolterephthalate. Suitable polyhydric alcohols include ethylene glycol,1,2- and 1,3 propylene glycol, 1,3- and 1,4-butanediol, 1,6-hexanediol,1,8-octanediol, neopentyl glycol, diethylene glycol,2-methyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol, thevarious isomeric bis-hydroxymethylcyclohexanes, glycerine andtrimethylolpropane.

2) Polylactones generally known from polyurethane chemistry, e.g.,polymers of e-caprolactone initiated with the above-mentioned polyhydricalcohols.

3) Polycarbonates containing hydroxyl groups such as the productsobtained from reaction of the polyhydric alcohols previously set forthfor preparing the polyhydroxy polyesters (preferably dihydric alcoholssuch as 1,3-propanediol, 1,4-butanediol, 1,4-dimethylol cyclohexane,1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethyleneglycol) with phosgene, diaryl carbonates such as diphenyl carbonate orcyclic carbonates such as ethylene or propylene carbonate. Also suitableare polyester carbonates obtained by the reaction of lower molecularweight oligomers of the above-mentioned polyesters or polylactones withphosgene,diaryl carbonates or cyclic carbonates.

4) Polyethers include the polymers obtained by the reaction of startingcompounds which contain reactive hydrogen atoms with alkylene oxidessuch as propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran,epichlorohydrin or mixtures of these alkylene oxides. Certainproportions of ethylene oxide may also be included, provided thepolyether does not contain more than 10% by weight of ethylene oxide;however, polyethers which do not contain ethylene oxide are preferablyused. Suitable starting compounds containing at least one reactivehydrogen atom include the polyols set forth as suitable for preparingthe polyhydroxy polyesters and, in addition, water, methanol, ethanol,1,2,6-hexanetriol, 1,2,4-butanetriol, trimethylol ethane,pentaerythritol, mannitol, sorbitol, methyl glycoside, sucrose, phenol,isononyl phenol, resorcinol, hydroquinone and 1,1,1- or1,1,2-tris(hydroxylphenyl)ethane. Polyethers which have been obtained bythe reaction of starting compounds containing amino groups can also beused, but are less preferred for use in the present invention. Suitableamine starting compounds include ethylene diamine, diethylene triamine,triethylene tetraamine, 1,6-hexanediamine, piperazine,2,5-dimethylpiperazine,1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, bis(4-aminocyclohexyl)methane, bis(4-amino-3-methylcyclohexyl)methane, 1,4-cyclohexanediamine,1,2-propanediamine, hydrazine, aminoacid hydrazides, hydrazides ofsemicarbazido carboxylic acids, bis-hydrazides and bis-semicarbazides,ammonia, methylamine, tetramethylenediamine, ethanolaminediethanolamine, triethanolamine, aniline, phenylenediamine, 2,4- and2,6-toluylenediamine, polyphenylene polymethylene polyamines of the kindobtained by the aniline/formaldehyde condensation reaction and mixturesthereof. Resinous materials such as phenol and cresol resins may also beused as the starting materials. The preferred starting compounds for thepolyethers are those compounds which exclusively contain hydroxylgroups, while compounds containing tertiary amine groups are lesspreferred and compounds containing isocyanate-reactive-NH groups aremuch less preferred.

In order to render the polyurethanes water-dispersible to enableformation of the dispersions of the present invention, it is necessaryto chemically incorporate hydrophilic groups, i.e., anionic groups,potential anionic groups or nonionic hydrophilic groups, into theisocyanate-terminated prepolymer component. Suitable hydrophiliccomponents contain at least one (preferably at least two) isocyanate orisocyanate-reactive group and at least one hydrophilic group orpotential hydrophilic group. Examples of compounds which may be used toincorporate potential ionic groups include aliphatic hydroxy carboxylicacids, aliphatic or aromatic aminocarboxylic acids with primary orsecondary amino groups, aliphatic hydroxy sulfonic acids and aliphaticor aromatic aminosulfonic acids with primary or secondary amino groups.These acids preferably have molecular weights below 400. It should beemphasized that the carboxylic acid groups are not considered to beisocyanate-reactive groups due to their sluggish reactivity withisocyanates.

The preferred anionic groups for incorporation into the polyurethanes inaccordance with the present invention are carboxylate groups and thesegroups may introduced by using hydroxy-carboxylic acids of the generalformula:

    (HO).sub.x Q(COOH).sub.y

wherein Q represents a straight or branched, hydrocarbon radicalcontaining 1 to 12 carbon atoms, and x and y represent values from 1 to3. Examples of these hydroxy-carboxylic acids include citric acid andtartaric acid.

The preferred acids are those within the above-mentioned formula whereinx=2 and y=1. These dihydroxy alkanoic acids are described in U.S. Pat.No. 3,412,054, herein incorporated by reference. The preferred group ofdihydroxy alkanoic acids are the α,α-dimethylol alkanoic acidsrepresented by the structural formula

    Q'--C(CH.sub.2 OH).sub.2 COOH

wherein Q' is hydrogen or an alkyl group containing 1 to 8 carbon atoms.The most preferred compound is α,α-dimethylol propionic acid, i.e.,wherein Q' is methyl in the above formula.

The acid groups may be converted into hydrophilic anionic groups bytreatment with a neutralizing agent such as an alkali metal salt,ammonia or primary, secondary or preferably tertiary amine in an amountsufficient to render the hydroxy functional polyurethanes waterdispersible. Suitable alkali metal salts include sodium hydroxide,potassium hydroxide, sodium hydride, potassium hydride, sodiumcarbonate, potassium carbonate, sodium bicarbonate and potassiumbicarbonate. The use of alkali metal salts as neutralizing agents isless preferred than the use of volatile organic compounds such asvolatile amines since they lead to reduced resistance to water swell inthe coatings or other ACES product produced from the water dispersiblecompositions of the present invention. Therefore, less than 50%,preferably less than 20% and most preferably none of the acid groupsshould be neutralized with alkali metals.

In addition, the use of tertiary amines that are relatively volatile ispreferred in order to facilitate easy removal of the tertiary aminecomponent during curing of the polyurethane composition. The preferredvolatile amines for neutralizing the acid groups are the tertiaryamines, while ammonia and the primary and secondary amines are lesspreferred. Examples of suitable amines include trimethyl amine,triethylamine, trisopropylamine, tributyl amine, N,N-dimethylcyclohexylamine, N,N-dimethylstearyl amine, N,N-dimethylaniline,N-methylmorpholine, N-ethylmorpholine, N-methylpiperazine,N-methylpyrrolidine, N-methylpiperidine, N,N-dimethylethanolamine,N,N-diethylethanolamine, triethanolamine, N-methyldiethanolamine,dimethylamionpropanol, 2-methoxyethyldimethylamine,N-hydroxyethylpiperazine, 2-(2-dimethylaminoethoxy)ethanol and5-diethylamino-2-pentanone. The most preferred tertiary amines are thosewhich do not contain isocyanate-reactive groups as determined by theZerewitinoff test since they are particularly capable of reacting withisocyanate groups during the curing of the compositions of the presentinvention on the desired substrate.

The acid groups on component (iii) of the isocyanate-terminatedprepolymer may be converted into hydrophilic anionic groups by treatmentwith the alkali metal or preferably the volatile amine either before,during or after their incorporation into the prepolymer. However, it ispreferred to neutralize the acid groups after their incorporation.

The polyisocyanate adduct useful in the present invention is suitably amixture, blend or separately added combination of polyisocyanate trimerand polyisocyante dimer. Suitable trimers include the isocyanurategroup-containing polyisocyanates prepared from the previously describedaliphatic and/or cycloaliphatic diisocyanates. Particularly preferredare isocyanato-isocyanurates based on 1,6-diisocyanatohexane and/or1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophoronediisocyanate or IPDI). The production of these isocyanurategroup-containing polyisocyanates is described, for example, in DE-PS2,616,416, EP-OS 3,765, EP-OS 10,589, EP-OS47,452, U.S. Pat. No.4,288,586 and U.S. Pat. No. 4,324,879. The isocyanato-isocyanuratesgenerally have an average NCO functionality of 3 to 3.5 and an NCOcontent of 5 to 30%, preferably 10 to 25% and most preferably 15 to 25%by weight.

Suitable dimers include uretdione diisocyanates prepared from thepreviously described aliphatic and/or cycloaliphatic diisocyanates. Theuretdione diisocyanates are preferably prepared from hexamethylenediisocyanate ("HDI") and/or of IPDI. Although, in theory, the uretdionediisocyanates can be used as the sole component of the polyisocyanateadduct, the present invention requires that at least some amount oftrimer also be present in the polyurethane dispersions of the presentinvention.

In addition to the combination of a dimer and trimer, urethane and/orallophanate group-containing polyisocyanates prepared from thepreviously described aliphatic and/or cycloaliphatic diisocyanates,preferably hexamethylene diisocyanate or IPDI, by reacting excessquantities of the diisocyanates with the previously described lowmolecular weight polyols, preferably trimethylol propane, glycerine,1,2-dihydroxy propane or mixtures thereof, are also suitably employed infabricating the polyisocyanate adducts, if desired. If used, theurethane and/or allophanate group-containing polyisocyanates have a mostpreferred NCO content of 12 to 20% by weight and an (average) NCOfunctionality of 2.5 to 3. Likewise, oxadiazinetrione groups can beemployed, if desired, in the preparation of the polyisocyanate adductsuseful in the present invention, such as, for example, those preparedfrom HDI.

A chain extending agent is also employed in accordance with the presentinvention.Examples of useful chain extenders or chain-lengthening agentsare low-molecular-weight polyols and polyamines. Examples of usefullow-molecular-weight polyols are glycols exemplified as materials forthe aforementioned polyester polyols and alkeylene oxide low-moleadducts thereof (less than 500 in molecular weight); alkylene oxidelow-mole adducts (less than 500 in molecular weight) of bisphenol;trihydric alcohols such as glycerin, trimethylolethane,trimethylolpropane and alkylene oxide low-mole adducts (less than 500 inmolecular weight) of such alcohols; and mixtures of at least two ofthese polyols. Examples of useful polyamines are aliphatic polyaminessuch as ethylenediamine, N-hydroxyethylethylenediamine,tetramethylenediamine, hexamethylenediamine and diethylenetriamine;alicyclic polyamines such as 4,4'-diaminodicyclohexylmethane,1,4-diaminocyclohexane and isophoronediamine; aliphatic polyamineshaving an aromatic ring, such as xylylenediamine andtetramethylxylylenediamine; aromatic polyamines such as4,4'-diaminodiphenylmethane, tolylenediamine, benzidine andphenylenediamine; and inorganic diamines such as hydrazine; and mixturesof at least two of these polyamines. The amount of the chain lengtheningagent is usually 0.3 to 30 wt. %, preferably 0.5 to 20 wt. %, based onthe high-molecular-weight polyol in preparing the prepolymer.

In order to reduce the viscosity of the water dispersiblepolyisocyanates an organic solvent may be added to the water dispersiblepolyisocyanate.

The aqueous coating compositions according to the present invention maybe applied to substrates using any of the various techniques known inthe art, and the coating compositions are particularly suitable for ACESapplications. In addition, the aqueous compositions may be blended withother types of resins optionally containing isocyanate-reactive groupsor with amine- or phenol-formaldehyde condensates known in the art. Theycan also contain pigments, levelling agents, catalysts, and otherauxiliaries known in the art. Examples of the application techniques,resins and auxiliaries are set forth in U.S. Pat. No. 4,408,008, whichis herein incorporated by reference.

The invention is further illustrated in, but is not intended to belimited by, the following examples in which all parts and percentagesare by weight unless otherwise specified.

EXAMPLE 1 (COMPARATIVE EXAMPLE)

Patent Literature Control Experiment--Coating Composition Prepared usingan IPDI-Terminated Prepared in Accordance with Example 1 of U.S. Pat.No. 5,169,895

Into a 2000 ml resins reactor equipped with stirrer, heating mantle,thermometer and nitrogen are charged 375 g (0.3790 eq.) on an ethyleneadipate diol, 28.05 g (0.4183 eq.) of dimethylol propionic acid (DMPA),165.9 g (1.265 eq.) dicyclohexylmethane-4,4'-diisocyanate (H₁₂ MDI),142.5 g of N-methyl-2-pyrrolidinone (NMP) and 0.6 g of dibutyl tindilaurate (DBTL). The system is stirred and heated to 80° C. for 2.5hrs. The reactor is cooled to 60° C. and maintained for 1.5 hrs and103.75 g (0.5337 eq.) Des N-100 (biuret of 1,6-hexane diisocyanate) and21.15 g (0.2090 eq.) of triethylamine (TEA) is added and maintained at60° C. for 1.5 hrs after which time 250 g of the pre-polymer reactionmixture is poured into 431.9 g water containing 2.5 g of Triton X-350surfactant. The mixture was mixed well on a drill press. After fiveminutes 7.37 g of 64% hydrazine is added and the mixture mixed well on adrill press. The final product is poured into a quart jar and cappedwith nitrogen.

Test specimens for physical property determination were made by drawingthin films on tin coated plates and on cold rolled steel plates coatedwith an ECOAT and a primer.

EXAMPLE 2

Coating Composition Made Using 1,6-hexane diisocyanate dimer/trimerVersus Control Experiment

This experiment was run under the same conditions and with the sameratio of reactants as the "Patent Literature Control Experiment" ofExample 1 above except the absolute amounts were scaled back to thoseindicated.

Into a 1000 ml resins reactor equipped with stirrer, heating mantle,thermometer and nitrogen are charged 158.02 g (0.157 eq.) on an ethyleneadipate diol, 11.82 g (0.1762 eq.) of dimethylol propionic acid (DMPA),70.65 g (0.533 eq.) dicyclohexylmethane-4,4'-diisocyanate (H₁₂ MDI),60.04 g of N-methyl-2-pyrrolidinone (NMP) and 0.25 g of dibutyl tindilaurate (DBTL). The system is stirred and heated to 80° C. for 2.5hrs. The reactor is cooled to 60° C. and maintained for 1.5 hrs and44.42 g (0.241 eq.) of 1,6-hexane diisocyanate dimer/trimer and 8.92 g(0.0881 eq.) of triethylamine (TEA) is added and maintained at 60° C.for 1.5 hrs after which time 316 g of the pre-polymer reaction mixtureis poured into 542.82 g water containing 3.16 g of Triton X-301surfactant. The mixture was mixed well on a drill press. After fiveminutes 9.31 g of 64% hydrazine is added and the mixture mixed well on adrill press. The final product is poured into a quart jar and cappedwith nitrogen.

EXAMPLE 3

Isophorone Diisocyanate Water Dispersed Urethanes 1,6-hexanediisocyanate dimer/trimer

Into a 1000 ml resins reactor equipped with stirrer, heating mantle,thermometer and nitrogen are charged 158.02 g (0.1597 eq.) on anethylene adipate diol, 11.82 g (0.1762 eq.) of dimethylol propionic acid(DMPA), 59.24 g of dibutyl tin dilaurate (DBTL). The system is stirredand heated to 80° C. for two hours. The reactor is cooled to 60° C. and44.42 g (0.241 eq.) 1,6-hexane diisocyanate dimer/trimer and 8.91 g(0.0881 eq.) of triethylamine (TEA) is added and maintained at 60° C.for one hour after which time 316 g of the pre-polymer reaction mixtureis poured into 542.82 g water containing 3.16 g of Triton X-301surfactant. Five minutes after the addition is complete 9.31 g of 64%hydrazine is added. The final product is poured into a quart jar andcapped with nitrogen.

EXAMPLE 4

1,6-hexane diisocyanate dimer/trimer with added dimer

Example #3 was repeated under identical conditions and using identicalreactants, except that the isocyanate was formulated to have a 25%higher dimer content.

EXAMPLE 5

Isophorone diisocyanate with no additional isocyanate added

Example #3 was repeated, but with the isophorone diisocyanate being theonly isocyanate present. The polyol used was a 1000 MW hexanediol adipicacid polyester diol.

EXAMPLE 6

Isophorone diisocyanate with added 1,6-hexane diisocyanate dimer/trimer

Example #3 was repeated with a blend of isophorone diisocyanate and1,6-hexane diisocyanate dimer/trimer as the isocyanate portion. Thepolyol used was a 1000 MW hexanediol adipic acid polyester diol.

As the results presented in Tables 1-6 below demonstrate, the additionof dimer/trimer provided films on a coated substrated having highermodulus and lower elongation, relative to films made using coatingcompositions not containing dimer/trimer. Abbreviations employed herein:

    ______________________________________                                        DMPA         Dimethylol propionic acid                                          H.sub.12 MDI Dicyclohexylmethane-4,4'-diisocyanate                            IPDI Isophorone diisocyanate                                                  HDI D/T 1,6-hexane diisocyanate dimer/trimer                                  NMP N-methyl-2-pyrrolidinone                                                  TEA Triethylamine                                                             DBTBL Dibutyltindilaurate                                                     QUV YI A yellowness index measurement of Q                                     ultraviolet light using ASTM E-313                                         ______________________________________                                    

                  TABLE 1                                                         ______________________________________                                        Comparison of Physical Properties of Coatings                                   Made from HDI/Biuret versus HDI/Dimer Trimer                                    Property         Example #1                                                                              Example #2                                     ______________________________________                                        Tensile Modulus psi at                                                          100% 2980 2590                                                                200% NA 3860                                                                  Tensile strength psi 3120 5800                                                Elongation  95  290                                                         ______________________________________                                         "NA" denotes not applicable.                                             

                  TABLE 2                                                         ______________________________________                                        Comparison of Mechanical Properties of Coatings                                 Made from HDI/Biuret versus HDI/Dimer Trimer                                  Test #      Property       Example #1                                                                            Example #2                               ______________________________________                                                  Thickness, mils                                                                              2         2                                            ASTM D-523-89 Gloss, 20° 83.2 82.3                                      60° 90.4 90.2                                                         ASTM D-3359 Adhesion Pass (5) Pass (3)                                        ASTM D-3363 Hardness, lead# 1 1                                               ASTM D-522 Conical Bend Pass Pass                                              Dry time, min 20 20                                                          ASTM D-2794 Impact                                                             Direct, ambient temp. 160+ 160+                                               Reverse, ambient temp. 160+ 160+                                              Direct, -17° C. 60 80                                                  Reverse, -17° C. 5 5                                                  ASTM E-313 QUV, Y.I., 0 hrs. -1.57 -1.52                                       QUV, Y.I., 2000 hrs. 0.33 0.36                                             ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Effect of Additional Dimer                                                                    Example #3                                                                              Example #4                                          ______________________________________                                        Polyol          158.02    158.02                                                DMPA 11.82 11.82                                                              IPDI 59.24 59.24                                                              DBTL 0.25 0.25                                                                NMP 60.04 60.24                                                               HDI D/T 44.42 34.17                                                           Additional HDI Dimer 0 10.25                                                  TEA 8.91 8.91                                                                 Prepolymer used 316 284.4                                                     64% Hydrazine 9.31 7.26                                                       Water 542.82 488.54                                                         ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Physical Properties of Coatings Made from HDI/Dimer                             versus HDI/Dimer with Added Dimer                                             Test Method Property      Example #3                                                                             Example #4                               ______________________________________                                        ASTM D-412                                                                              Tensile Modulus psi at                                                 100% 2220 2345                                                                200% 3510 3350                                                                300% NA 5415                                                                 ASTM D-412 Tensile strength psi 5110 7120                                     ASTM D-412 Elongation, %  270  357                                          ______________________________________                                         "NA" denotes not applicable.                                             

                  TABLE 5                                                         ______________________________________                                        Effect of 1,6-hexane Diisocyanate Dimer/Timer                                               Example #5                                                                              Example #6                                            ______________________________________                                        Polyol        100.59    100.59                                                  DMPA 14.16 14.16                                                              IPDI 63.74 63.74                                                              DBTL 0.30 0.30                                                                NMP 71.94 71.94                                                               HDI D/T 0 48.51                                                               TEA 9.69 10.68                                                                Prepolymer used 227.52 284.4                                                  64% Hydrazine 3.74 8.38                                                       Water 390.83 488.54                                                         ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Physical Properties of Coatings Made from IPDI                                  versus IPDI with Added HDI/Dimer                                                Property        Example #5                                                                              Example #6                                      ______________________________________                                        Tensile Modulus psi at                                                          100% 2105 4260                                                                200% 3650 NA                                                                  300% 5300 NA                                                                  Tensile Strength psi 5650 4720                                                Elongation, %  295  127                                                     ______________________________________                                         "NA" denotes not applicable.                                             

EXAMPLE 7

Incorporation of Dimer/Trimer directly into the prepolymer.

Into a 1000 ml resins reactor equipped with stirrer, heating mantlethermometer and nitrogen are charged 103.52 g (0.213 eq.) on an ethyleneadipate diol, 15.79 g (0.2354 eq.) of dimethylol propionic acid (DMPA),71.07 g (0.639 eq.) isophorone diisocyanate, 54.08 g (0.289 eq.)1,6-hexane diisocyanate dimer/trimer, 80.21 g ofN-methyl-2-pyrrolidinone (NMP) and 0.33 g of dibutyl tin dilaurate(DBTL). The system is stirred and heated to 80° C. for 4.0 hrs. Thecooled reaction mixture had an NCO content of 6.1%.

The pre-polymer reaction mixture, 284.4 g, is poured into 450.54 g watercontaining 2.84 g of Triton X-301 surfactant. The mixture was mixed wellon a drill press. After five minutes 9.82 g of 64% hydrazine is addedfollowed by a 30 g water rinse. The mixture is mixed well on a drillpress. The final product is poured into a quart jar and capped withnitrogen.

Test specimens for physical property determination were made by drawingthin films on tin coated plates and on cold rolled steel plates coatedwith an ECOAT and a primer.

                  TABLE 7                                                         ______________________________________                                        Mechanical Property Data                                                          Test #       Property       Example #7                                    ______________________________________                                                     Thickness, mils                                                                              1.2                                                 ASTM D-523-89 Gloss, 20° 95.5                                           60° 112.7                                                             ASTM D-3359 Adhesion Pass (5)                                                 ASTM D-3363 Pencil Hardness, lead # 4                                         ASTM D-522 Conical Bend Pass                                                   Dry Time, min 20                                                             ASTM D-2794 Impact                                                             Direct, ambient 110                                                           Reverse, ambient 160                                                          Direct, -17° C. 40                                                     Reverse, -17° C. 0                                                    ASTM E-313 QUV, Y.I., 0 hrs. -2.63                                             QUV. Y.I., 1056 hrs. 0.22                                                    ASTM D-412 Tensile Strength, pst 464.5                                        ASTM D-412 Elongation, % 62                                                 ______________________________________                                    

While the invention has been described above with reference to specificembodiments thereof, it is apparent that many changes, modifications andvariations can be made without departing from the inventive conceptdisclosed herein. Accordingly, it is intended to embrace all suchchanges, modifications and variations that fall within the spirit andbroad scope of the appended claims. All patent applications, patents andother publications cited herein are incorporated by reference in theirentirety.

What is claimed is:
 1. A method for coating a substrate which comprisescontacting the substrate with a coating composition comprising adispersion in water of the reaction product of:(a) a water-dispersibleisocyanate-terminated polyurethane prepolymer having an NCO content ofbetween about 1.5 and 10% by weight, said prepolymer having incorporatedtherein uretdione moieties and isocyanurate moieties, and (b) an activehydrogen-containing chain extender.
 2. The method of claim 1 wherein themolar ratio of said uretdione moieties to said isocyanurate moieties isbetween about 1:10 and about 10:1.
 3. The method of claim 1 wherein saidisocyanurate moiety is selected from the group consisting ofisocyanato-isocyanurates based on 1,6-diisocyanatohexane,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, andcombinations thereof.
 4. The method of claim 1 wherein said uretdionemoiety is selected from the group consisting of isocyanato uretdiones ofhexamethylene diisocyanate, isophorone diisocyanate, and combinationsthereof.
 5. The method of claim 1 wherein said water-dispersibleisocyante-terminated polyurethane prepolymer comprises the reactionproduct of:(i) an organic diisocyanate; (ii) a polyol componentcomprising a polymeric diol having a molecular weight in the range from250 to 5000, and (iii) a compound containing a hydrophilic center and atleast two isocyanate or isocyanate-reactive groups.
 6. The method ofclaim 5 wherein the compound of component (iii) is dihydroxyalkanoicacid.